Method of producing spheroidal agglomerates

ABSTRACT

A METHOD OF FORMING SHEROIDAL AGGLOMERATES OF PARTICLES IN WHICH OLEIC ACID IS MIXED WITH A POWDERED CERAMIC MATEIAL, ADDING TO THIS MIXTURE AMMONIUM HYDROXIDE, AND SUBSEQUENTLY AGITATING.

United States Patent Office 3,574,654 Patented Apr. 13, 1971 3,574,654METHOD OF PRODUCING SPHEROIDAL AGGLOMERATES Robert E. Cowan and E.Philip Ehart, Los Alamos, N. Mex., assignors to the United States ofAmerica as represented by the United States Atomic Energy Commission NoDrawing. Filed July 12, 1968, Ser. No. 744,319 Int. Cl. C09c 3/00 U.S.Cl. 106-309 Claims ABSTRACT OF THE DISCLOSURE A method of formingspheroidal agglomerates of particles in which oleic acid is mixed with apowdered ceramic material, adding to this mixture ammonium hydroxide,and subsequently agitating.

This invention described herein was made in the course of, or under, acontract with the U.S. Atomic Energy Commission.

Free-flowing powders are very advantageous when used in dry pressingsince they flow so easily. The process described herein has been usefulfor preparing a wide variety of materials such as setting sand forfiring ceramics and the dispersed second phase of an oxide in metalmatrices. In the first case, the spheroids are placed beneath a ceramicobject which is being fired. As shrinkage occurs, the spherical grainsallow the object to shrink uniformly.

In the second application, the fired spheroids are a dispersed secondphase of an oxide or carbide in a metal matrix. Such mixtures arefrequently used as fuel elements or control rods in nuclear reactors. Aspecific application is the preparation of boron carbide spheres by thismethod. These spheres will then 'be fired and incorporated into a coppermatrix for use as control rods in a nuclear propelled rocket.Free-flowing powders may be made by other methods such as spray drying,but these are more expensive and time consuming than the present method.

In the present invention, a saponification reaction is utilized in orderto form spheroidal agglomerates of inorganic particles. Moreparticularly, a small amount of fatty acid is thorughly mixed with apowdered, waterinsoluble inorganic material. A strong inorganic base inan amount sufficient to neutralize the acid is then added to the fattyacid and powdered material and then thoroughly mixed, tumbled, oragitated. The mechanical motion and reaction causes spheroidalagglomerates of small particles to form. The resulting particles (whichare really not particles, but rather loose agglomerates) are very freeflowing and spheroidal in shape.

It is therefore an object of this invention to provide a method forproducing spheroidal agglomerates of waterinsoluble inorganic material,and more specifically, an agglomerating process for ceramic-typematerial.

Other objects of this invention will be apparent from the followingdescription in which alumina, magnesia, and boron carbide materials areformed into spheroidal agglomerates using the method of this invention.

A specific procedure utilized in practicing this invention is asfollows:

Fused A1 0 powder is added to oleic acid in the amount of 2 ml. of oleicacid per 100 grams of A1 0 The A1 0 weighing 1500 grams is mixed withthe oleic acid in a twin shell blender. After thoroughly mixing theoleic acid in the A1 0 150 ml. of water is added, 50 ml. at a time,while the powder is being mixed. To this mixture 25 ml. of a 15 N NH OHsolution is added and mixing is continued for 5 minutes. At this point,the powder is observed to have agglomerated into spheroidal shapedparticles. The powder is then allowed to dry in air for 15 hours.

A second specific procedure utilizing the method of this invention andparticularly setting forth the parameters for the formation ofspheroidal agglomerates of magnesia is as follows:

Magnesia powder weighting 1500 grams is added to oleic acid in theamount of 1 ml. of oleic acid per grams of magnesia. The powderedmagnesia is placed in a twin shell blender to which appproximately ml.of water is added, 50 ml. at a time, while the powder is being mixed. Tothis mixture, 25 m1. of 15 N NH OH is added, and the mixing is continuedfor about 15 minutes. The resulting powder is observed to haveagglomerated into spheroidal shaped particles. At this point, theagglomerated powder is partially dried by an air blower for a period ofabout 6 hours.

A third specific procedure using the method of this invention is asfollows:

Boron carbide powder is added to oleic acid in the amount of 1 ml. ofoleic acid per 100 grams of boron carbide. Boron carbide powder weighing1500 grams and coated with the oleic acid is placed in a blender for aperiod of about 30 minutes. To this mixture is added 25 ml. of 15 N NHOH and 150 ml. of water. This resulting boron carbide powder is observedto have agglomerated into spheroidal shaped particles which are then airdried.

Although the invention has been described in particular as to alumina,magnesia, and boron carbide, it is within the scope of this invention toapply this process to any inorganic water-insoluble material. Further,although oleic acid and NH OH are the particular acid and base stated inthe three embodiments of this invention, it is to be understood that anymonobasic organic acid can be used and any strong inorganic base. Theamount of oleic acid needed is a function of the particle size of thestarting material; however, the inventors have found that less thanpercent by weight of the acid makes the process inoperative. Normally,1-3 percent by weight acid addition is sufficient, no surplus over thisamount being necessary, the larger amount being required for fineparticles (larger reacting area), less for coarse particles. Likewise,the tumbling or mixing time after the base has been added to theacid-coated ceramic is a function of the desired particle size, i.e.,the longer the mixing time, the larger the particle. The amount of waternecessary is about 10 percent by weight with more than 15 percent beingexcessive. A paste is formed when excessive water additions are usedrather than the spheroidal agglomerate. The drying times, as stated inthe various embodiments, are not critical and variations of same is afunction of the particle size, and furthermore, the invention is to belimited solely by the appended claims.

What we claim is:

1. A method of forming spheroidal agglomerates of inorganicwater-insoluble particles comprising mixing about 1 percent by weight ofoleic acid with a powdered inorganic water insoluble material selectedfrom the class consisting of alumina, magnesia, and boron carbide,adding 10-15 percent by Weight water and a sufi'icient amount of NH OHto react with the acid present, and subsequently agitating and dryingthe formed particles.

2. The method of claim 1 wherein the said waterinsoluble material isalumina.

3. The method of claim 1 wherein the said waterinsoluble material ismagnesia.

4. The method of claim 1 wherein the said waterinsoluble material isboron carbide.

5. The method of claim 1 wherein the amount of water added is 10 percentby Weight of the said material and the drying time is about 15 hours.

4 References Cited UNITED STATES PATENTS 2,987,412 6/1961 Csonka et a1.10 6-309X 3,223,482 12/1965 Puddington et a1. l06309X 3,333,980 8/1967McCord 306309X JAMES E. POER, Primary Examiner H. M. S. SNEED,Assisstant Examiner US. Cl. X.R. l06288B, 306

